BACKGROUND OF THE INVENTION

[0001] 1. Field of the Invention

[0002] The invention relates to a subrack for a composite subrack with two side walls, an upper side, an underside, a front side and a rear wall, for receiving modules. Furthermore, the invention relates to a composite subrack with at least two subracks arranged one vertically above the other, the subracks having two side walls, an upper side, an underside, a front side and a rear wall, for receiving modules.

[0003] 2. Description of the Related Art

[0004] A subrack is a casing which can receive a number of modules. In the case of a shielded subrack, the rear wall (backplane) of the subrack electrically interconnects the inserted modules and has integrated shielding layers, i.e., full-area electrically conducting planes, which are pressed as an integral part of the printed-circuit board and are electrically bonded to the casing at all the edges of the board. The wiring plate, like the metallic casing of the subrack, should be impermeable to inward or outward emission of high-frequency electrical waves. A removable front covering closes off the subrack on the operator side and a bottom plate and a top plate are perforated over a large area to achieve the highest possible throughput of air for dissipating the power loss of the modules, i.e., to achieve good cooling of the subrack.

[0005] In electrical terms, the subrack should form a Faraday's cage around the modules, since the aim is to avoid or shield the outward and inward emission of interference from and to these modules.

[0006] However, here the problem arises that the shielding effectiveness and cooling capability of the subrack act in a conflicting manner. To improve the cooling capability, the flow resistance to the air flowing through the subrack would have to be reduced. This can be achieved by increasing the openness of the perforation of the bottom and top plates. However, this is at the expense of a deterioration in the shielding effectiveness of the subrack.

[0007] If dissipation of the power loss by free convection is no longer possible, fans are fitted. However, this has the disadvantage that the fan units take up considerable space.

[0008] A composite subrack is a rack in which usually a number of subracks are fitted one vertically above the other. Each individual subrack draws in its cooling air from the underside and discharges it again in the upward direction. Consequently, each time it flows over into the next shielded subrack, the air passes two resistance zones, that is in each case the top plate and the bottom plate. If a composite subrack is fully occupied with eight two-tier subracks, the flow resistance is accumulated altogether sixteen-fold and an effective cooling capability is problematical.

SUMMARY OF THE INVENTION

[0009] It is therefore an object of the invention to develop a subrack for a composite subrack and to develop a composite subrack which provide an improvement in the cooling capability when the subracks are fitted into the composite subrack, without the electrical shielding of the modules within the subrack being impaired.

[0010] The object of developing a subrack and a composite subrack is achieved by a subrack for a composite subrack comprising: two side walls; an upper side; an underside; a front side; and a rear wall, for receiving modules, wherein both the upper side and the underside of the subrack are respectively provided with at least one clearance over a large area.

[0011] The object of the invention is also achieved by a composite subrack comprising: at least two subracks arranged one vertically above the other, the subracks constructed as described in the previous paragraph, and two shielding plates each shielding at least one large-area clearance, shielding at least one large-area clearance of the upper side of the upper subrack and shielding at least one large-area clearance of the underside of the lower subrack.

[0012] The subrack and composite subrack are explained in more detail below.

[0013] The inventors have realized that the top and bottom plates of the subracks located in the interior of the composite subrack are not required for electrical shielding of the modules if the composite subrack itself forms a Faraday's cage. Consequently, if these top and bottom plates are provided with clearances over a large area, they are then no longer relevant with regard to flowing of the air, or no longer hinder the free convection of the air, although the modules are still electrically shielded within the subrack.

[0014] In accordance with this realization, the inventors provide a further development of a subrack for a composite subrack with two side walls, an upper side, an underside, a front side and a rear wall, for receiving modules, to the extent that both the upper side and the underside of the subrack are respectively provided with at least one clearance over a large area. Advantageously, between three and nine large-area clearances are provided so that struts remain on the upper side and underside of the subrack that have a stabilizing effect.

[0015] This subrack according to the invention represents a basic element which no longer has EMC-effective (EMC=electromagnetic compatibility) restrictions on its upper side and on its underside.

[0016] In an advantageous configuration of the subrack according to the invention, the surface area of the at least one large-area clearance accounts for between 50% and 90%, preferably between 70% and 90%, of the entire surface area of the upper side or the underside of the subrack.

[0017] A further configuration of the subrack provides that webs, preferably edge webs, are provided on the upper side and on the underside of the subrack. The webs preferably have, at least partly, a perforation. This perforation can be used for example for fastening other parts to the subrack.

[0018] A particularly advantageous embodiment of the subrack according to the invention provides electrical bonding elements on the edge of each side wall of the subrack situated toward the upper side. These electrical bonding elements are designed in such a way that they can be snap-fitted onto the edges of the side wall.

[0019] Furthermore, the electrical bonding elements, which preferably comprise two comb-shaped springs, may be provided on the upper side, situated toward the front side of the subrack. These entities are preferably arranged in a U-shaped manner. The invention provides a strut which interconnects the side walls for fastening the springs on the subrack. The electrical bonding elements are fastened to this strut in an advantageous way, e.g., they are screwed on.

[0020] In another further development, further electrical bonding elements are provided on the upper side, situated toward the rear wall of the subrack. In a preferred embodiment, these entities have a triangular shape and can be fastened with the aid of a rail on the upper side of the subrack, the springs advantageously being merely pushed over the rail.

[0021] In a further development of the subrack according to the invention, a front covering with electrical bonding elements which bond the subrack is provided. The front covering closes off the subrack toward the operator side.

[0022] The electrical bonding elements are preferably of a flexible and electrically conducting design. For instance, the electrical bonding elements may take the form of a contact spring, preferably a metallic contact spring. Hereafter, too, bonding is understood as meaning electrical bonding.

[0023] A further advantageous configuration provides at least one, preferably two, shielding plates, which shield the at least one large-area clearance of the upper side and/or the underside of the subrack.

[0024] In an advantageous further development of the subrack according to the invention, the shielding plate has, at least partly, a perforation. As a result, simple mounting of the shielding plate on the upper side and the underside of the subrack is possible, for example via screws or rivets.

[0025] In addition, the shielding plate may have a multiplicity of regularly distributed holes (perforation), the entire open surface area of the holes (openness) lying in the range between 50% and 80%, preferably between 65% and 75%, of the entire surface area of the shielding plate. This open surface area of the holes is preferably as large as possible, to achieve an optimum cooling capability, the size of the holes being dependent on the frequency to be shielded. The higher the frequency, the smaller the size of the holes should be. An advantageous configuration of the shielding plate provides that, for shielding a frequency of 0 to 1 GHz, the holes of the shielding plate have a diameter of preferably around 4 mm.

[0026] To ensure the stability of the shielding plate, the distribution of the holes is dependent on the strength of the material used. In the case of high-strength materials, the open surface area of the holes may lie at the upper limit, that is to say at around 80%.

[0027] In addition, an optimum cooling capability depends on the extent of the perforated area. This extent preferably lies in the range between 80% and 95% of the entire surface area of the shielding plate.

[0028] Consequently, the configuration according to the invention of the shielding plate ensures not only a high air throughput through the subrack but also high electrical shielding. In particular, the frequencies of the mobile radio range are reliably shielded.

[0029] Furthermore, the shielding plate may have, at least at the edge facing toward the front side of the subrack, at least one, preferably more, bonding entity for the bonding of the shielding plate, at least to the subrack. The bonding entity is preferably in the form of a contact spring, which may be of a comb-like design.

[0030] With these configurations according to the invention, the subrack is then an EMC-effective casing, which represents a Faraday's cage for the modules within the subrack.

[0031] The inventors also provides further development of a composite subrack with at least two subracks arranged one vertically above the other, the subracks having two side walls, an upper side, an underside, a front side and a rear wall, for receiving modules, to the extent that at least two subracks, preferably all the subracks, are designed according to the invention, as described above, and, furthermore, two shielding plates are provided, shielding the upper side of the upper subrack and/or the underside of the lower subrack. The shielding plates are also designed according to the invention, as described above. The shielding plates are consequently attached according to the invention to the bottom of the lowermost subrack and the top of the uppermost subrack.

[0032] The intermediate planes required for the subrack guides (that is the upper sides and undersides of the subracks located in the interior of the composite subrack) are provided with clearances over a large area and are consequently no longer relevant with regard to flowing of the air, or no longer hinder the free convection of the air.

[0033] The construction of the composite subrack may consequently vary from two subracks to the full complement, that is, e.g., eight subracks. The invention also envisages retrofitting or exchanging of individual subracks in the composite subrack.

[0034] According to the invention, the height division of designs introduced is not exceeded, to provide downward compatibility. As a result, an exchange of subracks, old for new, is made possible, even if they are in the middle of the composite subrack. The height of the slot becoming free consequently advantageously corresponds to the height of the new subrack. The introduced designs of the existing subracks are consequently compatible with the subracks according to the invention.

[0035] Furthermore, the electrical bonding extends right over all the subracks, up to the ends of the composite subrack.

[0036] This consequently achieves the effect that the subracks according to the invention in the composite subrack can be coupled vertically to one another in such a way that they are electrically connected to form a single shielding casing. With the exception of the lowermost bottom plate and the uppermost top plate (which in each case may represent a shielding plate designed according to the invention), no further plates for shielding are required in the horizontal planes. The overall flow resistance is consequently reduced considerably and a high throughput of air is made possible.

[0037] A shielding plate with a known hole geometry, for example a 60° V-grid 5×4^φ, has a flow resistance of around 3. In comparison with modules with a target value below 8, it is evident that the flow resistance of two perforated plates is of the same order of magnitude and consequently significantly influences free convection. The composite subrack according to the invention acts in a way similar to a chimney and offers a distinctly increased cooling capacity.

[0038] An advantageous further development of the composite subrack according to the invention provides a connection frame between two subracks. The subracks according to the invention can then be retrofitted to existing known subracks to form composite subracks, so that a distinct improvement in the cooling capability is achieved by exchanging at least two or more subracks.

[0039] In a configuration of the composite subrack according to the invention, the connection frame has, at least partly, a perforation for fastening to one of the two adjacent subracks. The connection frame may be securely mounted, for example screwed, to the webs of the upper side or the underside of a first subrack.

[0040] Furthermore, according to the invention, the connection frame may have a multiplicity of bonding elements, which are arranged on the upper side or on the underside of the connection frame. The bonding elements in this case bond to the webs of the second subrack in such a way as not to produce a rigid mechanical connection.

[0041] This configuration achieves the effect of not forming a sizeable rigid arrangement, in order, on the one hand, to allow compensation for tolerances and on the other hand to permit the required freedom of movement in the event of mechanical stresses, that are caused, for example, by earthquakes.

[0042] The bonding element may in this case once again be of a flexible and electrically conducting design, preferably as metallic contact springs.

[0043] Another development of the composite subrack according to the invention provides that the connection frame has at least one bonding element at the edge lying toward the front side of the subrack, the bonding element bonding at least the underside of the upper subrack and the upper side of the lower subrack. With a closed front covering, this bonding element is additionally pressed into place and bonded by the bonding element of the front covering, so that the connection frame is also electrically connected to the front covering.

[0044] In an advantageous way, the bonding element is bent in a U-shaped form. Furthermore, there is also electrical conductivity and flexibility.

[0045] In a further advantageous embodiment of the composite subrack according to the invention, the connection frame comprises, at least partly, a C profile, the opening of the C profile facing inward. A fastening element can advantageously be lowered into the C profile.